Manufacture of vacuum electric incandescent lamps



July 22, 1941. E. L-EEDS EI'AL MANUFACTURE OF VACUUMELECTRIC INCANDESCENT LAMPS Filed Oct. 5, 1959 Inventor s: Reginald E. Leeds,

en" 'Attor'ng.

Patented July 22, 1941 MANUFACTURE OF VACUUM ELECTRIC INCANDESCENT LAltIPS Reginald E. Leeds and Marcello Pirani, Wembley,

England, assignors to General Electric Dompany, a corporation of New York Application ootober-s, 1939, Serial No. 298,138

In Great Britain September 30, 1938 ratus which may be employed in practicing our 4 Claims. Our invention relates to the manufacture of vacuum electric incandescent lamps, particularly to lamps of the elongated tubular type commercially known as the lumiline lamp wherein the filament extends along the greater part of the length of a tubular envelope whose length is many times its diameter. More particularly, our

invention relates to the gettering of such lamps.-

It is well known that lamps of the so-called ,flumiline type are difficult to clean-up by the usual process of providing a phosphorus getter in the neighborhood of the filament and running the lamp on an overload after it is sealed 011 from the exhausting pump. The reason is probably that, owing to charges on the envelope, it is difficult to develop the discharge. between the ends of the filament on which this process is known to depend. Nor is it possible to obtain-a satisfactory clean-up by passing a high-frequency discharge through the residual gas, for example by a Tesla coil.

We have found that it is possible to obtain a satisfactory clean-up by providing the lamp with an external electrode and appiying between.this

electrode and the filament (preferably heated toits normal operating temperature) an impi'lsive voltage, so as to cause to pass, through the residual gas a plurality of intermittent discharges separated by intervals long compared with the duration of each. The explanation of this fact does not,. of course, form part of. the invention; but it seems likely that, in accordance with the prevalent theory of gettering, the impulsive discharges form a surface adapted to absorb the gas and that the terval between-them is necessary in order that t e gas may diffuse to this surface to be absorbed here before it is subjected a later intervals appreciably lgr g as. compared to'the duration of each discharge- Further objects and advantages of our inven-- tion will appear from the following description I ofaspecles thereof.

The drawing is a atic view of appainvention.

According tothe invention, the manufacture of a lampof the type specified comprisesthe steps of providing within the envelope a suitable getter, exhausting the lamp, providing the lamp with an external electrode and applying between the said external electrode and an internal electrode (preferably the filament and preferably while the latter is heated to its normal operating temperature) an impulsive voltage, th duration .of each pulse being less than the interval between successive pulses. The lamp is preferably sealed oif before the impulsive voltage is applied, but' if desired, the sealing oif operation may be postponed, inknown manner, until after the clean-up or getterlng operation is completed. The external electrode may, of course, be merely temporary, and be removed after the clean-up is complete. Thus it may be a wire wrapped in a helix around the lamp envelope, or a split metal tube into which thelanip envelope is inserted. It need not surround the envelope completely; thus it may be an elongated plate extending along" the entire length of the envelope and curved so as to make contact with about one-third of the circumference of the envelope. The impulsive voltage may be generated by any known'means. If it is generated by 50-cycle. current, there are preferably not more than'two or three pulses per half @cle, The peak value of the impulsive voltage is preferably higher than the greatest overload that could besafely applied to the filament in the usual gettering process. Thus, if the lamp is designed for 250 volts, the peak of the pulse should be 400-600 volts. The discharges-producedby the impulsive voltage should be visibly luminous in suitably darkened surroundings.

In one embodiment of the invention, described by way of example, the envelope I0 is 220 long and 25 mm. in diameter. The filament spiral I l is 205 mm. long and is designed to operin the envelope, it is provided in the usuaimanate on 25 0 volts. Before the filament is mounted ner wltha phosphorus getter. After the lamp is exhausted; it is sealed off. A wire I! is wrapped in'a helix of some ten turns about the envelope.

Tlte secondary ii of a step-up iron-cored transformer II with /9000 turns .15 connected between the said wire it and the filament II by conductors II and II; the primary. I1 is fed from 250 A. C. terminals "-18 through a resistance I! of 2500 ohms in series with a capacity 20 of 0.5 mfd., a bee-hive argon filled glow lamp 2| being connected in parallel with the capacity and the primary. The filament H is heated by being connected directly to the 250 A. 0. means l8l8 by conductors 22, 23. The resistance l9 and capacity 20 and the striking voltage of the glow lamp 2| are adjusted so that one pulse of voltage is generated in the transformer I per half-cycle of the supply current.

-While we have found the method described hereinabove to beparticularly useful in connection with the manufacture of tubular incandescent lamps of the lumiline type, it has also been found to be advantageousin the manufacture of various other types of vacuum electric incandescent lamps, particularly lamps of the low-voltage type operating on less than 110 volts.

What we claim as new and desire-to secure by Letters Patent of the United States is:

1. A method of cleaning up the residual gases in a vacuum electric incandescent lamp having a filament mounted within an envelope contaim ing a quantity of getter material, which comprises adjusting an external electrode into close proximity to said envelope, and applying an impulsive voltage between said external electrode and said filament to thereby produce a plurality of intermittent discharges therebetween, the duration of each voltage impulse being appreciably less than the interval between successive impulses.

2. A method of cleaning up the residual gases in a vacuum electric incandescent lamp having a filament mounted within an envelope containing a quantity of getter'material, which comprises adjusting an external electrode into close proximity to said envelope, heating said filament to its normal operating temperature by passage of current therethrough, and applying an impulsive voltage between said external electrode and said filamentto thereby produce a; plurality of intermittent discharges therebetween, the

, duration of each voltage impulse being appreciably less than the interval between successive impulses.

3. A- method of manufacturing vacuum electric incandescent lamps which comprises mounting a filament within an envelope, inserting a quantity of getter material within said envelope, exhausting and sealing off said envelope, adjusting an external electrode into close proximity to said envelope, and applying an impulsive voltage between said external electrode and said filament to thereby produce a plurality of intermittent discharges therebetween, the duration of each voltage impulse being appreciably less than the interval between successive impulses.

4. A method of manufacturing vacuum electric incandescent lamps which comprises mounting a filament within an envelope, inserting a quantity of getter material within said envelope, connecting said envelope to a vacuum pump and exhausting said envelope, adjusting an external electrode into close proximity to said envelope, applying an impulsive voltage between said external electrode and said filament to thereby produce a plurality of intermittent discharges therebetween, the duration of each voltage impulse being appreciably less than the interval between successive impulses and sealing off said envelope.

REGINALD E. LEEDS. MARCELLO PIRANI. 

